Forming fibrous articles with a vacuum screen former with presser plates for smoothing the outside surfaces

ABSTRACT

A fibrous article is formed from a slurry by deposition on the walls of a vacuum screen former submerged within the slurry. Presser plates which are resiliently mounted to the screen former press and smooth the outside surfaces of the article under the action of the applied suction once the space between the plates and the screen former has become filled with the fibers. The applied suction can be supplemented or replaced by external pressure applied to the slurry surface.

United States Patent Dorril et al.

[ 1 March 6, 1973 FORMING FIBROUS ARTICLES WITH A VACUUM SCREEN FORMER WITH PRESSER PLATES FOR SMOOTHING THE OUTSIDE SURFACES Inventors: David Trevor Dorril, Kidderminster;

Charles Frank Cooper, Stourporton-Sevem, both of England Morganite Research and Development Limited, London, England Filed: Sept. 28, 1970 Appl. No.: 76,175

Assignee:

Foreign Application Priority Data Sept. 29, 1969 Great Britain ..47794/69 US. Cl. ..162/227, 162/387, 162/395,

162/415, 264/87 Int. Cl. ..D2lj 7/00 Field of Search ..162/220, 401, 389, 398, 396, 162/228, 227, 402, 387, 395, 415; 264/87, 313

[56] References Cited UNITED STATES PATENTS 503,284 8/1893 Keyes ..162/402 342,178 5/1886 Carmichael 2,106,440 l/l938 3,442,757 5/1969 Williams Primary Examiner-S. Leon Bashore Assistant Examiner-Richard H. Tushin Attorney-Larson, Taylor and Hinds [5 7 ABSTRACT A fibrous article is formed from a slurry by deposition on the walls of a vacuum screen former submerged within the slurry. Presser plates which are resiliently mounted to the screen former press and smooth the outside surfaces of the article under the action of the applied suction once the space between the plates and the screen former has become filled with the fibers. The applied suction can be supplemented or replaced by external pressure applied to the slurry surface.

4 Claims, 3 Drawing Figures PATENTEU R 75 m mt FORMING FIBROUS ARTICLES WITH A VACUUM SCREEN FORMER WITH PRESSER PLATES FOR SMOOTHING THE OUTSIDE SURFACES DESCRIPTION 1. Background of Invention This invention relates to shaping articles by the socalled vacuum forming or vacuum casting method.

Such a method is used, for example, in making papier mache articles from a slurry of paper pulp, and comprises collecting on a finely perforated or porous screen former a conglomerate of particles from a suspension of the particles in a fluid vehicle which is sucked through the former immersed in the suspension.

The conglomerate conforms by one surface thereof to the shape of the former on which the particles collect but this leaves the shape of the exposed opposite surface of the conglomerate dependent on the regularity or otherwise of the thickness of the conglomerate which thus has, at best, a somewhat rough finish on one surface.

Consequently, vacuum forming is only used for articles which require only one surface or side to be positively shaped.

The present invention provides a way of shaping more than one surface of a vacuum-formed article, for example both inside and outside surfaces of a hollow article.

2. Brief Statement of Invention According to the invention, at the higher pressure side of the screen former further from that at which suction is applied, there is provided a matrix which has a shape to form a required surface of the article and is spaced from the screen former by at least the required thickness of the article. The matrix is movable towards the screen former, and is arranged to yield under the effect of suction, so that the matrix can be caused to bear on and press the conglomerate of particles against the screen former.

The article is thus formed between and shaped at opposite surfaces by the screen former and matrix respectively.

The yielding action of the matrix or presser is automatic because initially, so long as the fluid vehicle has free access to the space between the screen former and the presser, the fluid pressure is the same at both sides of the presser but eventually, as such access becomes impeded by the accumulation of particles, the pressure in the space falls until the presser, according to the load at which it is arranged to yield, moves towards the screen former.

APPARATUS FOR CARRYING OUT THE INVENTION The screen former may be such as is known for vacuum forming and the presser may consist of one or more parts resiliently mounted on, or in relation to, the former, so as to be spaced therefrom initially by a gap larger than the thickness of the article to be made, and able to move under suction so as to sandwich conglomerate against the screen former.

For such a purpose as producing a smooth plane surface on the outside of a vacuum-formed article, the presser may be simply a plane rigid plate of which two opposite borders extend beyond the dimensions of the surface to be pressed and are connected to the screen former by resilient rubber mountings to give the required spacing and capability of yielding.

For more intricate shapes, the screen former or the presser, or both, are shaped, such as recessed or ridged, to provide the respective matrix for the required shape of the article. In accordance with the principles of moulding or casting technique, provision is made for removal of the article from the screen former and presser, such as by design for sliding withdrawal or construction of the screen former or presser in separable or collapsible parts.

FIELD OF USE OF INVENTION The invention is useful for the production of shaped refractory articles, such as gas fire radiants or foundry refractories, for example runner liners, elbows, valve or riser sleeves and insulation lids for crucibles. Such articles can be vacuum formed, with inner and outer surfaces of required shapes or finish, from a slurry of ceramic fibers with ball clay or other ingredients in water as the fluid vehicle.

Although the main purpose of the invention is surface-shaping, there are indications that it may provide ancillary advantages including a lower water content and a higher green strength" of formed articles, before they are fired. Also the articles may have a more uniform thickness, particularly at the edges of articles where particles can build up against the matrix, or presser, as well as against the screen former. Such build-up, or i i-filling, of edges or corners can promote eventual strength in an article at parts thereof which' may be required to be machined to finished shape.

Another use for the invention is in the forming of composites of high-strength fibers, for example boron fibers but preferably carbon fibers, such as are made by pyrolysis of filamentary organic material, particularly polyacrylonitrile, with a binder such as a synthetic resin.

In utilizing the invention for the production of such composites a so-called pre-preg, consisting of an initial formation of fibers and binder before setting, may be made using a liquid composition of the binder, such as dilute solution or a dispersion thereof, as the fluid vehicle. By selection of the binder content of the fluid vehicle and the degree of extraction thereof in the vacuum forming stage, the amount of binder incorporated with the fibers can be controlled so as to provide, for example, initial cohesion, for eventual further impregnation before curing or setting of the binder, or the final amount thereof.

In the use of the invention for such composites, the shape of the article formed may be simply a sheet or web, advantageously of controlled thickness and density, for lamination or other fabrication into a required article.

ILLUSTRATIVE EMBODIMENT OF THE INVENTION A preferred embodiment of the invention is illustrated, by way of example, on the accompanying drawing, in which:

FIG. 1 is a somewhat diagrammatic longitudinal section of a screen former used for making a simple boxsection gas fire radiant with pressed front and back surfaces,

FIG. 2 is an end elevation corresponding to FIG. 1, and

FIG. 3 is an isometric view of the formed radiant.

The drawing shows a screen former which is of closed-ended tapered box-sectional shape and consists of solid end walls 1 and 2 and water-permeable side walls 3 which may be made of fine mesh metal gauze on a supporting framework (not shown) or other perforated or porous material which will allow water to pass as through a fine screen. From the end wall 2 a pipe 4 is connected to a suction pump so that, when the screen former is immersed in a suitable ceramic fiberslurry, water will be extracted through the side walls 3 and pipe 4 causing fibers to conglomerate as a substantially uniform layer on the outside surfaces of the side walls 3. This is in accordance with known vacuumforming technique.

The present invention introduces shaping of the surface of the conglomerate facing away from the screen former. To achieve this, in the example illustrated, two presser plates 5 are provided which cover and are spaced from the upper and lower side walls 3 respectively. The plates 5 rest on resilient rubber end fillets 6, at opposite borders of the screen former end walls 1 and 2, and are embraced by rubber bands 7, one at each end, acting like garter springs to hold the plates 5 in place.

As the space 8 between each plate 5 and its opposed side wall 3 becomes progressively filled with a conglomerate of fibers, as indicated in FIG. 1, the consequent restriction of flow of water, under the effect of the suction applied through the pipe 4, will result in a lower fluid pressure existing in the space 8 than in the slurry outside the plate 5 which therefore will be subjected to a load tending to press it towards the opposed side wall 3. When the load is sufficient to compress the rubber fillets 6, the plate 5 bears on and presses the conglomerate of fibers the surface of which is thus caused to conform to the plate 5.

On each of the remaining two side walls 3, not provided with presser plates, fibers conglomerate in a layer 9, as indicated in FIG. 2, with the somewhat irregular surface typical of vacuum-formed articles.

On completion of the forming process, whichincidentally is indicated by an abrupt pressure drop in the suction line as the plates 5 close on to the conclomerate, the complete assembly is removed from the slurry, the plates 5 are removed and the conglomerate body is stripped from the former for subsequent drying and baking treatment in the usual way.

It has been noted in practice that often the presser plates 5 separate themselves from the opposed surfaces of the conglomerate when the suction process has removed the major part of the water from the conglomerate.

As shown by FIG. 3, the shaped radiant has smooth faces 10, formed by the plates 5, somewhat irregular sides 11, as usual on a vacuum-formed article, and an inside surface 12 which is a cast of the surface .of the screen former side walls 3. At the ends of the faces 10,

relatively smooth edges 13 are produced by pressure of the conglomerate against the rubber fillets 6.

ALTERNATIVE EMBODIMENTS OF THE INVENTION Although the invention has been described as applied to forming articles by the use of suction, other means could be used to obtain the pressure differential required for the fluid vehicle to pass through a screen former. For example su'ction applied at one side of the former could be supplemented or replaced by pressure applied to or produced in the fluid vehicle at the other side of the former.

Since the matrix and screen former are submerged in the fluid, the fluid pressure differential at the start of the process is exerted across the screen former only. As the conglomerate grows on the screen former, the pressure is exerted across the screen former and conglomerate. When the conglomerate substantially fills the space between the matrix and the screen former, the pressure is exerted across the matrix as well and the matrix is thus urged against the conglomerate by the differential pressure.

We claim:

1. A method of making an article by filter casting, comprising:

providing submerged in asuspension of material to be cast a screen former and a matrix, said matrix being resiliently mounted for movement relative to the screen former and spaced from it by a distance determining the thickness of the article;

applying a differential pressure across the screen former; allowing casting to proceed until a conglomerate of cast material substantially fills the space between the matrix and the screen former, whereupon the pressure differential comes to act across the matrix, conglomerate and screen former as a whole rather than across the growing conglomerate and the screen former only;

after said space is substantially filled, allowing the matrix to move towards the screen former, under the action of the differential pressure, to form the article by bearing against and shaping the conglomerate by conformation thereof to the opposed faces of the matrix and screen former;

removing the article so formed from the matrix and screen former.

2. A method according to claim 1, in which resilient means for yieldingly mounting the matrix are arranged between the screen former and matrix so as to define the conglomerate laterally.

3. A method according to claim 2, in which the particles are fibrous particles in a liquid vehicle.

4. A method according to claim 3, in which the liquid vehicle is a binder for the fibrous particles and the resilient means yieldingly mounting the matrix are arranged to yield under the effect of the fluid pressure differential so as to control the residual binder content of the conglomerate. 

1. A method of making an article by filter casting, comprising: providing submerged in a suspension of material to be cast a screen former and a matrix, said matrix being resiliently mounted for movement relative to the screen former and spaced from it by a distance determining the thickness of the article; applying a differential pressure across the screen former; allowing casting to proceed until a conglomerate of cast material substantially fills the space between the matrix and the screen former, whereupon the pressure differential comes to act across the matrix, conglomerate and screen former as a whole rather than across the growing conglomerate and tHe screen former only; after said space is substantially filled, allowing the matrix to move towards the screen former, under the action of the differential pressure, to form the article by bearing against and shaping the conglomerate by conformation thereof to the opposed faces of the matrix and screen former; removing the article so formed from the matrix and screen former.
 2. A method according to claim 1, in which resilient means for yieldingly mounting the matrix are arranged between the screen former and matrix so as to define the conglomerate laterally.
 3. A method according to claim 2, in which the particles are fibrous particles in a liquid vehicle. 